Welcome to Indonesia's Swallow Birds Nest factory town

The tiny port of Kumai on the southern tip of Indonesian Borneo is a burgeoning trade centre in one of the world's most valuable animal products - the nests used for Swallow Birds Nest.

Drab concrete buildings have sprouted up all across Kumai, towering above the traditional low-rise shop-houses.
The buildings have no windows - instead they have many tiny holes. They are in fact birdhouses, or more accurately, Swallow Birds Nest factories.
Kumai's human population is about 20,000. Its population of swiftlets - the tiny birds whose nests are so valuable to the Chinese - must be 10 times that number.
They cover the sky, thrashing about and letting out screeches that are audible in every part of town.
The explosion in the bird population has come as an irritation to some in Kumai.
"The Chinese started building birdhouses here about 10 years ago," says a local park ranger.
"At first it was fine, but now it's taking over the whole town. The people don't have much of a say. Local politicians just let it happen." 

Welcome to Indonesia's swallow birds nest factory town

Tasteless, but wholesome

The edible nests, which the birds make from their saliva, have been a part of Chinese cookery for more than 1,000 years.
They can be used in sweet or savoury dishes.
Food writer and broadcaster Ching-He Huang says one way of preparing the nests is to slow cook them with rock sugar, allowing them to take on the flavours of other ingredients.
But she explains that the nests are revered for their reputed medicinal benefits and cultural importance rather than their flavour.
"Many Chinese women I know have it because the gelatinous texture of the Swallow Birds Nest is said to be very good for maintaining youth - it's thought to help collagen production," she says.
"The sweet version is delicate. It's like drinking a thick jelly-like soup. It can be served as a dessert or on its own."
The dark damp caves of South East Asia's tropical regions provide the natural habitat for the swiftlets.
Indonesia has many such caves, and has a long history in the Swallow Birds Nest trade. As far back as the 17th Century there are records of the trade in the archipelago.
For most of that time, the nests were collected from caves by skilled climbers using flimsy bamboo trellises.

Lucky charms

According to local legend, the practice of farming the birds in houses grew up accidentally several generations ago, when a local landowner in Sedayu, in East Java, left his house to go on the Hajj pilgrimage, says Ani Mardiastuti, from Bogor Agricultural University.
"He went to Hajj for several months, and some of his rooms were closed. When he came back from Hajj, he found that the swiftlets had been using his rooms for nesting," she says.
"Later on, he imitated the condition of the swiftlet room in other rooms, and he succeeded, so inventing the technique to farm the swiftlet."
Bird farmers are still notoriously secretive about how they attract the animals - but part of the method appears to be playing recordings of the swiftlets' song.
Reports abound of industrious Indonesians trying anything from lucky charms to casting spells in an effort to lure the birds into their buildings.

From caves, to cities

But for much of the 20th Century the trade was relatively small, and was dominated by traditional nest collectors.
China's authoritarian Communist ruler Mao Zedong denounced the soup as a decadent luxury, so almost the entire world market was in Hong Kong.
The soup only started to regain popularity on the mainland during the 1990s, but experts say it has now overtaken Hong Kong as Indonesia's main export market.
As demand has risen, concrete birdhouses have been erected throughout Indonesia, Malaysia, Thailand, Vietnam and most recently Cambodia.
The birds have willingly moved to the cities, and the high-rise accommodation provided for them, complete with birdsong on the CD player.
Some environmentalists have warned that other species of swiftlets with less desirable nests may suffer, and have also expressed concern that the industry is entirely unregulated.
But for the swiftlets with edible nests (known as white-nest swiftlets), the industry's development is no bad thing, says Richard Thomas from the Oriental Bird Club.
"A lot of new habitats and breeding areas have been created, and there seems to be a good understanding that if you take the nests away too often, the birds will not build new ones," he says.
"Also, as the industry moves more into the cities and away from the caves, it allows the other bird populations to live undisturbed in their natural habitats."
The surge in demand has forced the prices up from about $400 (£250) a kilo (the equivalent of about 120 nests) in the mid-1990s to $3,000 a kilo for the highest quality nests on today's market.
Indonesia reportedly made $226m in 2009 from the industry, and dominates the world market.
So the birds are happy, Chinese foodies are happy, and most importantly, the taxman is happy. The complaints of locals may just be drowned out for the time being.